The present invention relates to a method and apparatus for aligning the drill stem and bit of a rock drill rig when the drilling procedure starts.
When drilling holes in a rock for blasting or other purposes it is important that each hole extends in a correct direction. However, the hole may be formed in a wrong direction even if the drill stem has been correctly adjusted and positioned before the drilling procedure starts. Such faulty drilling mainly has two causes. On one hand, this faulty drilling may happen because the drill stem and bit are pushed against the rock at such a high feeding power that the articulated and extensible drill boom, as well as the pivotally supported feed support of the rock drill rig, are bent or deformed with the resut that the drill stem and bit are caused to extend in a wrong direction. On the other hand, the drill bit may slip sideways along an uneven rock surface and thus bring the drill stem out of its correct direction. In addition to being aligned in an incorrect direction, the drill stem may in both cases be exposed to bending which will reduce its useful life.
Due to the practical geometry of the drill boom, a perfect correction of the direction of the drill stem and bit requires adjustment on preferably all axes of the boom. This correction conventionally is performed manually, and often is measured by sight. Possible instrumentation in this connection has hitherto been limited to a means that shows the direction of the feed support. Manual adjustment of the drill, with or without such a means, is a difficult operation and the result is to a great extent dependent on the ability and attention of the operator. When drilling peripheral holes in particular, high requirements are placed an the operator because the direction of the drill stem is then especially important, since these holes determine the shape of the cavity to be blasted.
When the drill stem has been formed in a wrong direction, the operator of today has to adjust the stem by sighting from the operator's seat on the drill rig. In many situations when drilling in tunnels, however, visual observation of the direction and of the bend of the drill stem is almost impossible because sighting is hindered by the drill boom and support.